EGR systems are employed by internal combustion engines to help reduce various engine emissions. A typical EGR system may include a conduit, or other structure, fluidly connecting some portion of the exhaust path of an engine with some portion of the air intake system of the engine to thereby form an EGR path. Different amounts of exhaust gas recirculation may be desirable under different engine operating conditions. In order to regulate the amount of exhaust gas recirculation, such systems typically employ an EGR valve that is disposed at some point in the EGR path.
Systems have been developed to control EGR flow by regulating the amount of exhaust gases that are recirculated under various operating conditions, e.g., by controlling the position of an EGR valve. Some systems include an actuator for opening and closing the EGR valve, wherein the actuator is controlled by software-implemented control logic. Depending on the operating conditions of the engine, the control logic may position the EGR valve to allow varying amounts of exhaust gases to be recirculated.
While larger amounts of exhaust gas recirculation (i.e., higher EGR flow rates) may, under certain engine operating conditions, reduce emissions, various components may be affected by the EGR flow rate and, as such, may be taxed beyond their operating limits if EGR flow rates get too high. Exemplary components and/or engine operating parameters that can be affected by EGR flow rate may include turbo chargers, engine temperature, exhaust temperature, exhaust pressure, catalytic converters, particulate traps, air-to-air after coolers (ATAAC), EGR coolers, etc. In addition, condensation of gases in the air intake track of the engine may also become problematic at higher EGR flow rates.
EGR systems have been developed that are configured to monitor one or more operating conditions of engines and vary the amount of exhaust gas recirculation based on these monitored conditions. For example, U.S. Pat. No. 6,868,824, issued to Yang et al. (“the '824 patent”), discloses a system configured to control EGR flow rate based on parameters such as exhaust pressure, exhaust temperature, and turbo speed. However, the system of the '824 patent does not control the EGR flow rate based on monitored operating parameters related to the EGR system itself, such as air-to-air after cooler (ATAAC) inlet temperature, EGR cooler inlet temperature, or levels of condensation of gases in the air intake track of the engine. Therefore, none of these components are directly protected by the EGR control system. Although, in some circumstances, limiting EGR flow rate based on other parameters may protect one or more of these components, without directly monitoring the operating parameters of the EGR system components, it is possible for these components to be taxed beyond their operating limits without detection. Further, the system of the '824 patent does not determine maximum EGR flow rates for each of the monitored components under various operating conditions and control EGR flow rate to prevent exceeding the lowest of the determined maximum EGR flow rates.
The present disclosure is directed at solving one or more of the problems discussed above.